Abstract: NC II(10´6) experiment derived from crossing between 10 indica-japonica chromosome segment substitution lines (CSSLs) with uniform japonica genome background and 6 japonica testers was conducted to analyze GCA, SCA, and relative genetic parameters of target chromosome segments. The GCAs of 10 CSSLs in main yield-component traits except 1000-grain weight were higher than those of background parent. CSSLs AIS84, AIS27, AIS3, AIS80, and AIS76 with chromosome substitution segments respectively from chromosomes 12, 4, 1, 11, and 11 ranked the top 5 in GCA of yield-related characters. The results indicated that heterosis of main yield-component traits in indica/japonica combinations at chromosome segment level was much stronger than that of typical japonica hybrid rice and intentionally substituting japonica chromosome segments with indica coun-terparts of X24-2–R367 (Chr. 12), R1854–R288 (Chr. 4), C970–C955 (Chr. 1), C1350–R257 (Chr. 11), and X52–R2913 (Chr. 11) could significantly upgrade yield potential of japonica hybrid rice. The SCA of different combinations with one same parent or different traits in the same combination had significant difference and the combinations with top SCA or bottom SCA could be derived from different parental GCA groups, which show that there is no causal relation between SCA and parental GCA. High GCA combining with strong SCA is a basic principle of parent selection in super-high yield hybrid rice breeding.

Key words: Rice, CSSL, Inter-subspecific heterosis, Combining ability